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"Yesterday I got a TB skin test, but now I only have a black and blue spot. Is that normal?"

Zocdoc›Answers›Yesterday I got a TB skin test, but now I only have a black and blue spot. Is that normal?

Question

It is my first tb test and as far as i know i have not been anywhere near someone with tb.

Answer

I suggest that you return to your primary care physician or other practitioner for your TB reading on time. A skin TB test (also known as a PPD) is a test to look to see if you have been exposed to the tuberculosis bacteria in the past. The idea is to inject a protein that looks like part of the TB bacteria. If you have been exposed to TB already, your immune system will recognize it an attack that area of the skin thinking that the TB bacteria are there. The skin will become red and inflamed. If you have not been exposed, then your immune system will not recognize it. The black and blue spot is just a bruise from the injection. It really means nothing other than the injection broke a blood vessel. It happens frequently.
Again, please return to your primary care physician or other practitioner for your TB reading on time. This should be between 48 and 72 hours after you have the PPD placed. If you wait longer, then it will need repeated. If it looks red or raised, they might decide to measure it. If its under a certain diameter or if there is no redness at all, then you will be cleared. If redness develops and its over a certain diameter, then you will need to have a chest x-ray to look for any spot that could be TB. After that, you will need a treatment based on the findings. I should note that this is a fairly unusual occurrence in the US. Please discuss with your physician.

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Zocdoc Answers is for general informational purposes only and is not a substitute for professional medical advice. If you think you may have a medical emergency, call your doctor (in the United States) 911 immediately. Always seek the advice of your doctor before starting or changing treatment. Medical professionals who provide responses to health-related questions are intended third party beneficiaries with certain rights under Zocdoc’s Terms of Service.